This invention relates to reciprocating piston engines and more particularly to a balancer for balancing a second order pitching couple in such an engine.
In the design of an inline five cylinder engine, it was recognized that the arrangement resulted in a second order vertical pitching couple acting on the engine frame as a result of the action of crankshaft rotation and the reciprocation of the connected reciprocating masses. In order to provide a smoother running engine, it was considered desirable to provide a suitable balancer for the engine to create an opposing couple that would balance out the pitching couple developed by the operating components of the engine.
The present invention combines with the engine a balancer having dual, oppositely rotating balance shafts that create oppositely rotating unbalance couples which combine to apply a vertical pitching couple to the associated engine frame that opposes and balances the pitching couple developed in the engine rotating and reciprocating components. While the balancer has been developed for a specific five cylinder engine arrangement, it could also be utilized in other engines in which an unbalanced pitching couple is present.
The balancer is driven by a sprocket carried adjacent the rear end of the engine crankshaft and engaging a chain which drives first and second driven sprockets. A first balance shaft is mounted to one side of the engine frame and is directly connected with the first sprocket for rotating the balance shaft in the direction of the crankshaft at twice crankshaft speed. A second balance shaft is mounted to an opposite side of the engine frame and is indirectly connected to the second sprocket through a reversing drive for rotating the second balance shaft in a direction opposite to that of the crankshaft and at twice crankshaft speed. The balance shafts each have longitudinally-spaced, oppositely facing balance weights that develop equal and oppositely rotating unbalance couples. These couples combine to generate a vertical pitching couple equal to and opposing the second order pitching couple of the engine.
In a preferred embodiment, the reversing drive includes a drive gear rotatable with the second sprocket and engaging a driven gear carried on the second balance shaft. The two gears provide the reversal of direction of the balance shaft to a rotation opposite that of the crankshaft and at twice crankshaft speed. Preferably, the gears are carried by a mounting plate on fixed centers and the mounting plate is made of a ferrous material similar to the gears to maintain a relatively constant gear backlash at various operating temperatures.
Because of the gear drive, the balance weights of the second balance shaft are designed with smaller diameters to provide a critical mass polar moment of inertia that avoids rotational vibrations in the shaft and resulting gear tooth mismotion and rattle during operation in the range of engine speeds. For this purpose, the balance weights of the second balance shaft are made longer and of smaller diameter than the balance weights of the first balance shaft. The first balance shaft has larger diameter weights and is shorter than the second balance shaft to minimize the space occupied by the first balance shaft.
The chain drive includes a chain tensioner to control chain motion during engine operation. The arrangement is such that the chain, the driven sprockets and the gear components are mounted on a rear wall of the engine frame and the drive sprocket is carried on the crankshaft adjacent a rear end thereof.
These and other features and advantages of the invention will be more fully understood from the following description of certain specific embodiments of the invention taken together with the accompanying drawings.